Muscle atrophy occurs with disuse, muscular dystrophy, glucocorticoid treatment (as in Cushing's syndrome), and with many systemic diseases (e.g. cancer cachexia, diabetes, fasting), when overall rates of protein degradation exceed protein synthesis. Most types of atrophy have a general increase in degradation of intracellular proteins mainly through the ubiquitin(Ub)-proteasome pathway and share a common set of transcriptional changes. Currently, no effective pharmaceutical treatments for atrophy are available. Work on proteasome inhibitors and the transcriptional regulation of the Ub- proteasome pathway has suggested that the proteasome is an excellent target. However, my recent studies with cell culture suggest that the lysosomal (autophagic) process also contributes to protein loss. Studying mouse models of muscle wasting with very different causes (denervation, glucocorticoid administration, and mdx mice - a muscular dystrophy), I have three aims. 1) To determine to what extent the lysosmal and proteasomal pathways contribute to denervation and glucocorticoid-induced atrophy, I will use specific inhibitors of these pathways while measuring overall protein degradation rates in incubated muscles. 2) To learn how Velcade, a specific proteasome inhibitor approved for cancer therapy, can influence protein breakdown during denervation atrophy in adult mice, I will quantify muscle protein fractions, isometric contractile ability in incubated muscle and determine the molecules that activate these pathways by using real-time PCR and Western blotting for known transcription factors or ubiquitin ligases. (Denervation atrophy would be expected to be activated via the FOXO transcription factors or possibly through NFkB.) 3) To explore the efficacy of Velcade administraction to mdx mice, I will test whether Velcade, which can increase dystrophin content, can improve dytrophic muscle contractile function in isolated muscles and whether the increased content of mutant dystrophin it due to specific effects on this short-lived protein or a result of effects on overall protein degradation (by Western blotting and specific protein degradation assays). Taken together, these studies should advance our long-term goal of developing viable therapies for muscle wasting. RELEVANCE. Muscle wasting is an often debilitating complication of muscle disuse, fasting and many systemic diseases such as cancer, AIDS, or muscular dystrophy. Since these muscle atrophies share many common features, our research on therapies and mechanisms of slowing protein breakdown may lead to a viable treatment for these individuals.